In a major development toward the understanding of the biology of depression, researchers have identified 15 regions of the human genome associated with depressive illness.

Investigators conducted what's known as genome-wide association studies involving nearly 500,000 people, comparing genetic variations of those who said they had suffered from depressive symptoms with people who said they had not.

The newly discovered regions will give scientists places to look in the human genome where specific depression genes may lurk.

Until now, it's been a challenge identifying genes that are responsible for mood disorders because of the hundreds of thousands of genetic variants that scientists suspect are involved.

Each gene confers a small amount of risk of developing depression, said Roy Perlis, director of the Center for Experimental Drugs and Diagnosis at Massachusetts General Hospital in Boston, and a co-author of the study, published in the journal Nature Genetics.

Healthy people have some of these variations, he said, but if enough genes are involved, depression can be the result.

"Our primary interest is how do we go from finding these genes, to making new kinds of treatments so we can better treat depression," Perlis said.

The lifetime risk of developing a major depressive disorder, experts say, is anywhere from 15 to 20 percent.

Symptoms of depression range from sadness, loss of appetite and lack of enjoyment in life to mood swings.

Pinpointing specific sites

Until now, Perlis says research has focused on a small number of targets in the brain.

The data involved in the latest study came from an organization called 23andMe, a company that specializes in creating genetic profiles for people wanting to learn more about their ancestry.

In this case, the information was from individuals of European descent who agreed to participate in the studies.

Investigators sifted through the entire genomes of the participants, comparing genetic variations between the two groups.

A detailed analysis revealed more than a dozen genomic regions that increase a person's risk for depression, including 17 specific sites containing genes implicated in the mood disorder.

Some of the sites pinpointed by researchers are located in or near genes involved in brain development.

Two gene regions had been previously identified. One of the regions for depression had been associated with epilepsy and intellectual disability. Another contained a poorly understood gene in the brain. The latest analysis identified them as being significantly associated with depression.

‘Reduce the stigma’

The next step, Perlis says, is to look at other ethnic groups to try to identify brain regions that play a role in development of mood disorders.

"Because the more we can illustrate to people that these are brain diseases, that they are affected by genes that influence brain development, my hope is that it will start to reduce the stigma that goes along with depression,” he said. “So that in this sense, I hope this will have an immediate impact."

But don't expect new treatments for mood disorders anytime soon. According to Perlis, the discoveries are only the beginning of what will continue to be an ongoing exploration for the biological underpinnings of depression.